3-Azabicyclo(3.1.0)hexane-2-carboxylic acid has been found to be an effective plant male gametocide: U.S. Pat. No. 4,047,930 (the compound is designated therein as 2-carboxy-3,4-methanopyrrolidine). The compound exists in the forms of two geometric (i.e., cis, trans) isomers. Each of these isomeric forms exists in the form of optical isomers. The L,cis isomer occurs naturally in the seeds of the American horse chestnut, Aesculus parviflora and is active as a plant male gametocide. The racemic mixtures of both of the geometric isomeric forms are active as plant male gametocides.
3-azabicyclo(3.1.0)hexane-2-carboxylic acid can be prepared by:
(1) reducing 3-azabicyclo(3.1.0)hexan-4-one-2-carbonitrile to form 3-azabicyclo(3.1.0)hexane-2-carbonitrile; PA0 (2) converting the 3-azabicyclo(3.1.0)hexane-2-carbonitrile to 3-azabicyclo(3.1.0)hexane-2-carboxylic acid:
(a) by treating the nitrile with barium hydroxide to form the barium salt of the acid, then treating the salt with sulfuric acid; PA1 (b) by treating the nitrile with hydrochloric acid.
This process is the subject matter of applications Ser. Nos. 14,528 and 26,150. The product of the process ordinarily is a mixture of the racemates of the two geometric isomeric forms.
For various reasons, it is desirable that there be available a method for spearating one of the geometric isomeric forms from the other.